Patent reference 1 discloses a production method of a 4-oxoquinoline compound represented by the formula [III]:
wherein each symbol is as described in the patent reference 1 (hereinafter sometimes to be abbreviated as compound [III]), and specifically, the following production methods are known.Production Method 1-1 (See Patent Reference 1: Page 67)

Each symbol in the scheme is as described in the patent reference 1.
This production method is also described in patent reference 2, page 64 (each symbol in the scheme is also described in patent reference 2).
Production Method 1-2 Example of Production Method Using Compound [9] Having a Hydroxyl-Protecting Group (See Patent Reference 1: Page 71)

Each symbol in the scheme is as described in patent reference 1.
This production method is also described in patent reference 2, page 68 (each symbol in the scheme is also described in patent reference 2).
Production Method 2-1 (See Patent Reference 1: Page 72)

Each symbol in the scheme is as described in patent reference 1.
This production method is also described in patent reference 2, page 69 (each symbol in the scheme is also described in patent reference 2).
Production Method 2-2 Example of Production Method Including Introduction-Removal Step of Hydroxyl-Protecting Group (See Patent Reference 1: page 74)

Each symbol in the scheme is as described in patent reference 1.
This production method is also described in patent reference 2, page 72 (each symbol in the scheme is also described in patent reference 2).
Production Method 3 (See Patent Reference 1: Page 76)

Each symbol in the scheme is as described in patent reference 1.
This production method is also described in patent reference 2, page 74 (each symbol in the scheme is also described in patent reference 2).
Production Method 4 (See Patent Reference 1: Page 77)
Examples of production methods of the above-mentioned compound [12] are more concretely given below.

Each symbol in the scheme is as described in patent reference 1.
Production Method 5 (See Patent Reference 1: Page 79)

Each symbol in the scheme is as described in patent reference 1.
The production method is also described in patent reference 2, page 78 (each symbol in the scheme is also described in patent reference 2).
The above-mentioned production method 1-1 and production method 2-1 respectively relate to a production method of compound [1-2] and compound [1-5] corresponding to the above-mentioned compound [III].
The production method 1-2, production method 2-2 and production method 5 show production examples including introduction-removal of hydroxyl-protecting group.
In addition, production method 3 discloses a method for introducing a substituent after formation of a 4-oxoquinoline ring, and production method 4 describes examples of production method of compound [12] more specifically.
Moreover, patent reference 1 discloses, as one of the compounds particularly useful as anti-HIV agents from among compounds [III], 6-(3-chloro-2-fluorobenzyl)-1-((S)-1-hydroxymethyl-2-methylpropyl)-7-methoxy-4-oxo-1,4-dihydroquinoline)-3-carboxylic acid (hereinafter sometimes to be abbreviated as compound (10)) and a production method thereof.
Specifically, Example 4-32 in patent reference 1 describes the following production example.
In addition, production of 2,4-difluoro-5-iodobenzoic acid (starting material) is disclosed in patent reference 1, Example 4-33, step 1.
wherein NIS is N-iodosuccinimide, Catalyst is a catalyst, and the other symbols are as defined in patent reference 1.
This production method is also described in patent reference 2, page 112, Reference Example 9.
As a production method similar to this production method, patent reference 3 describes, at page 23, Example 2-1, a production method wherein the hydroxyl-protecting group is a tert-butyldimethylsilyl group. Further, patent reference 3, page 12, Reference Example 1; page 17, Example 1 and page 39, Example 2-4 describe a method of directly producing compound (10) from a compound wherein a hydroxyl-protecting group is tert-butyldimethylsilyl group, as shown below.

Moreover, patent reference 1, page 81, Reference Example 1, or patent reference 2, page 80, Reference Example 1 disclose that 2,3-dichlorobenzylzinc chloride which is an analog of 3-chloro-2-fluorobenzylzinc bromide produced in the above-mentioned step 6, can be produced in the same manner from 2,3-dichlorobenzyl chloride.

Patent reference 3 discloses a production method of compound (10).
Specifically, patent reference 3 describes the following production example in Example 2-2, page 28.
wherein DBU is 1,8-diazabicyclo[5.4.0]undecene, Catalyst is a catalyst, and the other symbols are as defined in patent reference 3.
While patent reference 1, patent reference 2 and patent reference 3 disclose production methods of compound (10), the production methods embrace the following aspects.                In the final step (alkoxylation, particularly methoxylation), a dimer is by-produced depending on the base to be used. In this event, a removal step of the by-produced dimer is further necessary, which decreases the yield greatly.        When sodium fluoride by-produced in the final step (alkoxylation, particularly methoxylation) is acidified in the treatment step, hydrofluoric acid is produced and corrodes the production facility. Thus, a removal operation of sodium fluoride is essential and the operation is complicated.        There is a concern about an unfavorable influence of hydrofluoric acid produced in the ring-closing step on the production facility, and therefore, the method is not of a level satisfactory as an industrial production method.        Removal of the product by-produced in a reaction to insert compound [IIb] is complicated (since alkylzinc derivative is used together with a palladium catalyst, an operation to remove zinc salt and palladium salt as impurities is necessary and the operation is complicated).        Plural operations are necessary to protect hydroxyl group with methyl chloroformate in a preliminary step of the reaction to insert compound [IIb], and to deprotect the group in a later step, and the operation is complicated.        A step using 3-chloro-2-fluorobenzyl bromide for the production of compound [IIb] is not beneficial for industrial production, since the compound shows high tearing property.        
The above-mentioned production method including these steps is associated with many aspects to be improved for industrial production, and the development of a more superior production method of compound (10) is desired.
In addition, while non-patent reference 1 describes the following benzoic acid compound and the like, it provides no description of the compound (2′) of the present invention to be explained in detail in the following.

Moreover, patent reference 4 describes, in the ring-closing reaction for forming a 4-oxoquinoline skeleton, a production example of a 4-oxoquinoline skeleton from the following acrylic acid ester and the like. However, it provides no description of the production method of compound (9) from compound (7), or compound (8) from compound (6-B) of the present invention to be explained in detail in the following.

Patent reference 5 (see page 11, compound 2-12) describes the following benzoic acid compound [A] and the like as photosensitive materials. However, it provides no description of the compound (2′) of the present invention to be explained in detail in the following.

Moreover, non-patent reference 2 describes the following benzoic acid compound [B] and the like (see scheme 2). However, it provides no description of the compound (2′) of the present invention to be explained in detail in the following.

In addition, non-patent reference 3 describes the following benzoic acid compounds [C] and [D] and the like (see page 3512, compounds 10 and 12). However, it provides no description of the compound (2′) of the present invention to be explained in detail in the following.
                [Patent reference 1] WO 04/046115        [Patent reference 2] WO 05/113509        [Patent reference 3] WO 05/113508        [Patent reference 4] U.S. Pat. No. 4,695,646 (column 15, line 40)        [Patent reference 5] JP-A-11-84556        [Non-patent reference 1] Zhurnal Organicheskoi Khimii, vol. 6, number 1, pages 68-71, 1970 (page 70, 3)        [Non-patent reference 2] Synlett, vol. 5, p. 447-448, 1996        [Non-patent reference 3] Macromolecules, vol. 28, p. 3509-3515, 1995        